This invention relates to polycarbonate block copolymers and especially to flame retardant polycarbonate block copolymers.
Polycarbonate resins are useful in high temperature applications because they exhibit excellent high heat performance. It is therefore important for these resins and/or resin compositions to be flame resistant. Previously, flame resistance has been achieved with the addition of flame retardants, generally halogenated flame retardants or halogenated blocks within the polycarbonate polymer chain. The addition of flame retardants increases the cost of the materials, and plastics employing halogenated materials may release toxic gas when heated to elevated temperatures. As a result, non-halogenated fire resistant materials, especially those that are transparent, are in demand for a wide range of applications.
Copolymers having organopolysiloxane blocks and polycarbonate blocks are known. U.S. Pat. No. 3,419,635 to Vaughn, incorporated by reference herein, discloses room temperature vulcanizing organopolysiloxane-polycarbonate block copolymers and methods of making them. The organopolysiloxane-polycarbonate block copolymers are useful in elastomeric applications. U.S. Pat. No. 6,072,011 to Hoover also discloses block copolymers useful as molding resins comprising polycarbonate blocks and polysiloxane blocks. In contrast to the compositions disclosed in Vaughn, the compositions as taught by Hoover are thermoplastic. Neither composition is disclosed to be transparent, and the compositions of Hoover as taught in the examples employ a halogenated fire retardant.
Accordingly, there is a need in the art for non-halogenated, highly fire resistant polycarbonate resins, especially polycarbonate resins that are transparent and exhibit excellent high heat performance.
The above described drawbacks and deficiencies are overcome or alleviated by a block copolymer comprising structural units of the formula (I): 
wherein R1 comprises polysulfone groups, and structural units of the formula (II): 
wherein R2 comprises polysiloxane groups.
A block copolymer comprises structural units of the formula (I): 
in which R1 comprises polysulfone groups, and structural units of the formula (II): 
wherein R2 comprises polysiloxane groups. The block copolymer may further comprise structural units of the formula (III): 
wherein R3 comprises aromatic and/or aliphatic groups. The structural units of formula (I) are hereinafter referred to as the polysulfone structural units. The structural units of formula (II) are hereinafter referred to as the polysiloxane structural units. The structural units of formula (III) are hereinafter referred to as the aromatic/aliphatic structural units. The polysulfone structural units and polysiloxane structural units and, when present, the aromatic/aliphatic structural units may be arranged in a random sequence or in a non-random repeating sequence. Typically the polysulfone structural units comprise about 80 weight percent to about 99.9 weight percent of the block copolymer. The polysiloxane structural units typically comprise about 0.1 weight percent to about 20 weight percent of the block copolymer. When it is desired for the block copolymer to be transparent, the polysiloxane structural unit content is preferably less than about 4.6 weight percent of the block copolymer. The aromatic/aliphatic structural units, when present, comprise about 0.1 weight percent to about 98 weight percent of the block copolymer. The block copolymer may have an average molecular weight, Mw, in the range of about 10,000 to about 100,000, with a range of about 25,000 to about 35,000 preferred.
The block copolymer is preferably made by the reaction of a carbonate precursor, such as phosgene, dihydroxy polysulfone oligomer(s) and dihydroxy polysiloxane oligomer(s). When the block copolymer comprises aromatic or aliphatic, structural units as well as polysulfone structural units and polysiloxane structural units it is preferably made by the reaction of a carbonate precursor, such as phosgene, dihydroxy polysulfone oligomer(s), dihydroxy polysiloxane oligomers and dihydroxy aromatic and/or dihydroxy aliphatic compound(s). It is also possible that the block copolymer may be made by other methods known in the art for making polycarbonates such as transesterification as disclosed in U.S. Pat. No. 3,154,008.
Useful dihydroxy polysulfone oligomers include dihydroxy aromatic polysulfone oligomers. An aromatic polysulfone oligomer is defined as a polyarylene compound in which an arylene unit, an ether unit, and a sulfone bond are essential constitutional units and in which the arylene units are disorderly or orderly arranged together with the ether and sulfone bonds. Suitable arylene units include substituted and unsubstituted phenylene, napthylene, and other multi-cyclic aromatic compounds as well as divalent aromatic moieties of the formula:
xe2x80x94A1xe2x80x94Y1xe2x80x94A2xe2x80x94
wherein A1, Y1, and A2 are described below.
It is preferred that the hydroxyl functionalities be located terminally although it is within the scope of the invention for one or both hydroxyl functionalities to have a non-terminal location. Non-terminal is herein defined as being located in a position other than at the end of the oligomer chain. Useful molecular weights of dihydroxyl aromatic polysulfone oligomers are about 500 to about 10,000. Dihydroxyl aromatic polysulfone oligomers with a molecular weight of about 2,000 to about 3,500 are preferred.
A preferred aromatic polysulfone oligomer comprises repeating units characterized by the general formula: 
wherein useful values for n are in the range from 1 to about 10.
An especially preferred hydroxyl terminated aromatic polysulfone oligomer has the formula 
wherein n is equal to approximately 5. The especially preferred hydroxyl terminated aromatic polysulfone oligomer is well known and can be made by the reaction of dichlorodiphenylsulfone and bisphenol A wherein bisphenol A is present in slight excess.
Useful dihydroxy polysiloxane oligomers include, but are not limited to hydroxyl terminated poly(dialkylsiloxane)oligomers comprising repeating units of the general formula: 
wherein R4 and R5 are selected independently from saturated and unsaturated hydrocarbons having 1 to about 15 carbons, including alkyl groups, alkylene groups, and aryl groups. Preferably, R4 and R5 are methyl or phenyl. The number of repeating units can range from 0 to about 120. Preferred dihydroxy polysiloxane oligomers are terminated by a substituted or unsubstituted hydroxy aromatic group, wherein the substituents may be halo, aryl, alkyl, alkylene, alkoxy or aryloxy groups having from 1 to about 15 carbons. Especially preferred dihydroxy polysiloxane oligomers are phenol or eugenol terminated. A preferred eugenol terminated polysiloxane oligomer has the formula: 
with m=0-47 and R6-11 selected independently from saturated and unsaturated hydrocarbons having 1 to about 15 carbons, including alkyl groups, alkylene groups, and aryl groups. Preferably, R6-11 are methyl or phenyl.
Useful dihydroxy aromatic or aliphatic compounds comprise from 2 to about 50 carbons. Preferably the dihydroxy compound is an aromatic dihydroxy compound with the formula
HOxe2x80x94A1xe2x80x94Y1xe2x80x94A2xe2x80x94OH
wherein each of A1 and A2 is a monocyclic aryl group and Y1 is a bridging group having one or two atoms which separate A1 from A2. In an exemplary embodiment, one atom separates A1 from A2. Illustrative non-limiting examples of groups of this type are xe2x80x94Oxe2x80x94, xe2x80x94Sxe2x80x94, xe2x80x94S(O)xe2x80x94, xe2x80x94S(O)2xe2x80x94, xe2x80x94C(O)xe2x80x94, methylene, cyclohexyl-methylene, 2-[2.2.1]-bicycloheptylidene, ethylidene, isopropylidene, neopentylidene, cyclohexylidene, cyclopentadecylidene, cyclododecylidene, and adamantylidene. The bridging group Y1 can be a hydrocarbon group or a saturated hydrocarbon group such as methylene, cyclohexylidene or isopropylidene.
Especially preferred are bisphenol compounds having general formula (VIII) as follows: 
wherein Ra and Rb each represent a halogen atom or a monovalent hydrocarbon group and may be the same or different; p and q are each independently integers from 0 to 4; and Xa represents one of the groups of formula (VII): 
wherein Rc and Rd each independently represent a hydrogen atom or a monovalent linear or cyclic hydrocarbon group and Re is a divalent hydrocarbon group.
Some illustrative, non-limiting examples of suitable dihydroxy compounds include the dihydroxy-substituted aromatic hydrocarbons disclosed by name or formula (generic or specific) in U.S. Pat. No. 4,217,438, which is incorporated herein by reference. A nonexclusive list of specific examples of the types of bisphenol compounds that may be represented by formula (VI) includes the following:
1,1-bis(4-hydroxyphenyl)methane;
1,1-bis(4-hydroxyphenyl)ethane;
2,2-bis(4-hydroxyphenyl)propane (hereinafter xe2x80x9cbisphenol Axe2x80x9d or xe2x80x9cBPAxe2x80x9d);
2,2-bis(4-hydroxyphenyl)butane;
2,2-bis(4-hydroxyphenyl)octane;
1,1-bis(4-hydroxyphenyl)propane;
1,1-bis(4-hydroxyphenyl)n-butane;
bis(4-hydroxyphenyl)phenylmethane;
2,2-bis(4-hydroxy-1-methylphenyl)propane;
1,1-bis(4-hydroxy-t-butylphenyl)propane;
bis(hydroxyaryl)alkanes such as 2,2-bis(4-hydroxy-3-bromophenyl)propane;
1,1-bis(4-hydroxyphenyl)cyclopentane; and
bis(hydroxyaryl)cycloalkanes such as 1,1-bis(4-hydroxyphenyl)cyclohexane.
It is preferable to include, during synthesis of the block copolymer, an endcapping or terminating agent. The use of endcapping agents is well known in the art and all known endcapping agents are useful, especially aromatic compounds with a single hydroxyl group such as phenol, alkyl substituted phenol and napthol. Useful amounts of endcapping agents are about 0.1 to about 2.0 weight percent.
The block copolymers of the invention may be employed without further admixture, or after admixture with various additives. Such additives are known to the art of plastics compounding, and may include, for example, about 0.5 to about 20 parts by weight of a filler or a reinforcing agent; about 0.01 to about 0.1 part by weight of a heat stabilizer; about 0.01 to about 0.2 part by weight of an antioxidant; about 0.1 to about 0.7 part by weight of a light stabilizer; about 0.5 to about 3 parts by weight of a plasticizer; about 0.1 to about 3 parts by weight of an antistatic agent; and about 0.1 to about 1 part by weight of a mold releasing agent. The above amounts of the additives are based on 100 parts by weight of the polycarbonate resin.
Examples of the filler or reinforcing agent include glass fibers, asbestos, carbon fibers, silica, talc and barium sulfate.
Examples of the heat stabilizer include triphenyl phosphite, tris-(2,6-dimethylphenyl)phosphite, tris-(mixed mono- and di-nonylphenyl)phosphite, dimethylbenzene phosphonate and trimethyl phosphate.
Examples of antioxidant include octadecyl-3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate, and pentaerythrityl-tetrakis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate].
Examples of the light stabilizer include 2-(2-hydroxy-5-methylphenyl)benzotriazole, 2-(2-hydroxy-5-tert-octylphenyl)-benzotriazole and 2-hydroxy-4-n-octoxy benzophenone.
Examples of the plasticizer include dioctyl-4, 5-epoxy-hexahydrophthalate, tris-(octoxycarbonylethyl)isocyanurate, tristearin and epoxidized soybean oil.
Examples of the antistatic agent include glycerol monostearate, sodium stearyl sulfonate, and sodium dodecylbenzenesulfonate.
Examples of the mold releasing agent include stearyl stearate, beeswax, montan wax and paraffin wax.
Such additives may be mixed at a suitable time during the mixing of the components for forming the composition.
The block copolymer is typically synthesized by charging a polymerization vessel with dihydroxy polysulfone oligomer, dihydroxy polysiloxane oligomer, optional aromatic or aliphatic dihydroxy compound, organic solvent, water, a base, typically an organic base, with sufficient basicity to remove the proton from the hydroxyl functionalities, and an endcapping agent and stirring the resulting mixture vigorously. Phosgene is bubbled through the solution at a rate sufficient to enable the polymerization reaction to proceed, generally about 5 grams/minute to about 75 grams/minute. The rate of phosgene bubbling is dependent upon the reaction conditions and is readily determined by one of ordinary skill in the art. Aqueous sodium hydroxide is added, preferably continuously, in order to maintain the pH of the solution between about 8 and about 11. The reaction is complete when the product has reached the desired molecular weight. The molecular weight can be determined by gel permeation chromatography or any other means known in the art. When the reaction is complete, the organic layer is separated from the aqueous layer, washed with dilute hydrochloric acid followed by deionized water. The solvent is then removed and the resulting colorless materials can be handled by all method known in the art, including, precipitation, extrusion, and molding.
The invention is further illustrated by the following non-limiting Examples.